Question

Select the incorrect statement from the following: (a) Neural signal from pneumotaxic centre can reduce the duration of inspiration. (b) The role of oxygen in the regulation of respiratory rhythm is quite significant. (c) RBCs contain a very high concentration of the enzyme, carbonic anhydrase and minute quantities of the same is present in the plasma too. (d) \(\mathrm{CO}_{2}\) is carried by haemoglobin as carbamino-haemoglobin (about \(20-25\) per cent).

Short answer

The incorrect statement is: (b) The role of oxygen in the regulation of respiratory rhythm is quite significant.

Step-by-step solution

Analyze Statement (a)

The pneumotaxic center sends out neural signals to the diaphragm, effectively counteracting the apneustic center, and consequently reducing the duration of inspiration. Therefore, statement (a) is correct, as it accurately describes the function of the pneumotaxic center.

Analyze Statement (b)

Oxygen as such does not directly regulate the respiratory rhythm; it is actually the concentration of carbon dioxide in the blood that majorly influences the rate and depth of breathing, as high levels of carbon dioxide lead to increased breathing rate. Thus, statement (b) is incorrect as it overstates the role of oxygen in the regulation of respiratory rhythm.

Analyze Statement (c)

Red blood cells do contain a high concentration of carbonic anhydrase, an enzyme that catalyzes the conversion of carbon dioxide and water to carbonic acid, a reversible, and crucial reaction in the transport of carbon dioxide from the tissues to the lungs. Small amounts of this enzyme are also present in the plasma. Hence, statement (c) is correct.

Analyze Statement (d)

Approximately 20-25% of carbon dioxide in the blood is carried by hemoglobin as carbamino-hemoglobin. This is a correct fact about the transport of carbon dioxide in the blood, making statement (d) correct.

Key concepts

Neural Control of Respiration

The control of your breathing doesn't just happen randomly; it's governed by specialized areas in the brain. The primary centers responsible for this are the pneumotaxic and apneustic centers, which are located in the pons of the brainstem.
The **pneumotaxic center** is a critical player in regulating how long you inhale each breath. It sends signals to stop the inhalation process, ensuring that your breaths are not too long. This center essentially puts a "cap" on the inspiratory phase, helping maintain the rhythm of breathing. Without this, breath or inspiration could become unwieldy long, leading to inefficient intake of air and oxygen.
Conversely, the **apneustic center** helps initiate and extend inhalation. It's like the opposite of the pneumotaxic center, lengthening the breathing phase so the body gets enough air.
Together, these centers work like a finely-tuned orchestra, ensuring that breathing is smooth, rhythmic, and responsive to the body's needs.

Oxygen and CO2 Transport

Transporting oxygen and carbon dioxide in the body involves a delicate balance between the bloodstream and respiratory system. Oxygen is primarily transported in the blood by being loosely bound to hemoglobin within red blood cells (RBCs). This allows oxygen to be transported efficiently to tissues that need it.
Carbon dioxide, a waste product from metabolism, is transported in three major ways:

• Dissolved CO2: A small amount of carbon dioxide is simply dissolved in the plasma.
• Carbamino compounds: Approximately 20-25% of CO2 binds to hemoglobin, forming carbamino-hemoglobin. This form is crucial for transporting CO2 back to the lungs to be exhaled.
• Bicarbonate ions: The majority of carbon dioxide is transported in the form of bicarbonate ions, created with the help of the enzyme carbonic anhydrase.

Overall, these mechanisms ensure efficient exchange and transport of gases.

Role of Carbonic Anhydrase

Carbonic anhydrase is an enzyme found abundantly in red blood cells and in smaller amounts in plasma. Its main role is to catalyze the conversion of carbon dioxide and water into carbonic acid, which is essential for the transport of CO2.
This reaction is crucial because carbonic acid quickly dissociates into bicarbonate ions and hydrogen ions:
\[ ext{CO}_2 + ext{H}_2 ext{O} \rightleftharpoons ext{H}_2 ext{CO}_3 \rightleftharpoons ext{HCO}_3^- + ext{H}^+\]
These bicarbonate ions are then transported in the bloodstream to the lungs. In the lungs, the reaction can reverse, allowing CO2 to be expelled as you exhale. Without carbonic anhydrase, the conversion between CO2 and bicarbonate ions would be too slow to handle the body's metabolic needs efficiently.

Carbamino-Hemoglobin

Carbamino-hemoglobin forms when carbon dioxide binds to hemoglobin in red blood cells. This process accounts for about 20-25% of the total carbon dioxide transport in the bloodstream.
Instead of binding to the iron atom in hemoglobin like oxygen, carbon dioxide attaches to the protein part of the molecule. When tissues produce carbon dioxide during metabolism, this CO2 is picked up by hemoglobin as carbamino-hemoglobin, carrying it back to the lungs.
Once in the lungs, the carbon dioxide is released from the hemoglobin so it can be exhaled. This mechanism is efficient and ensures that CO2 is removed from the body continuously as a by-product of metabolism.
This dual ability of hemoglobin to carry both oxygen and carbon dioxide is vital for maintaining metabolic processes and acid-base balance in the body.